The invention relates generally to electric-actuated automotive emission control valves, and more particularly to an exhaust gas recirculation (EGR) valve for an internal combustion engine that powers an automotive vehicle.
An EGR valve may comprise a solenoid as an electric actuator. The solenoid comprises an electromagnet coil and a stator having an air gap at which magnetic flux acts on an armature. The armature motion is transmitted to a valve member to allow flow through a passageway of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve member, to bias the armature to a position that causes the valve member to close the passageway.
In a linear solenoid valve, displacement of the armature, and also of the valve member when the valve member is displaced in exact correspondence with the armature, should theoretically bear a relationship of direct proportionality to the electric current in the solenoid coil. In other words, a graph plot of armature displacement versus electric current for such a valve should start at the origin of the graph and extend from the origin at a constant slope. For any one or more of various reasons that will be discussed, a graph plot of armature displacement versus electric current for an actual linear solenoid valve is apt not to correspond with the theoretical graph plot that would define an ideal linear solenoid valve.
A known linear solenoid EGR valve comprises a stator having an upper stator part that is disposed at an upper end of the coil and a lower stator part at the lower end of the coil. These two parts have respective cylindrical walls, one tapered and the other non-tapered, that fit into the open center of the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two walls are spaced apart within the open interior of the coil, and their construction and arrangement define an annular air gap disposed circumferentially around the armature. Electric current in the coil creates magnetic flux that passes from one wall across the air gap to the armature, through the armature, and back across the air gap to the other wall. The flux causes magnetic force to be applied to the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid. While certain changes in coil current will change the magnetic flux spanning the air gap, armature displacements resulting from those current changes may also change the magnetic flux pattern, the flux density, and/or how that flux density acts on the armature, and it is such changes that may impart non-linearity to a desired linear relationship of armature displacement to coil current.
The particular construction and arrangement of the juxtaposed walls of the upper and lower stator parts that define the air gap, and the need to create a certain minimum current flow in the solenoid coil before any displacement of the armature can occur, are two causes for a valve to have a displacement versus current characteristic that departs from a perfectly linear one. Certain conditions that are present at initial valve opening but not thereafter, such as static friction and less than perfect pressure compensation, and the force that must be exerted by the return spring to assure that the valve is closed when no current flows in the coil, are causes of valve non-linearity. The need to build a certain minimum electric current in the coil before any armature displacement can occur creates an inherent offset in a graph plot of armature displacement versus coil current. Because of the offset, graph plot of armature displacement versus coil current cannot pass through the origin of the graph, and so the plot will be inherently non-linear even if the plot has a constant slope once the armature displacement begins. Additional non-linearity would be manifested by variations in slope of the graph plot.
Where flow through the valve is proportional to armature displacement, the functional relationship of flow to electric coil current will have similar non-linearity. In an EGR valve, such non-linearity may complicate the control strategy for accurately metering exhaust gas into the engine intake system over the flow range involved for the engine.
It would therefore be desirable if improved definition and better linearity could be obtained in the functional relationship of valve opening to coil current in an actual linear solenoid valve, and especially at initial valve opening and over a contiguous range of relatively smaller valve openings. It is believed that such improvements would be especially beneficial when metering small amounts of exhaust gas for engine exhaust gas recirculation.
It would also be desirable to provide a basic valve construction that can be adapted by valve designers to create actual valves possessing desired functional characteristics conforming to customer specifications.
It is an object of this invention to satisfy such desires.
One general aspect of the invention relates to an emission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and an electric actuator for selectively positioning the valve element. The actuator comprises a solenoid having an electromagnet coil and a stator associated with the coil, and the stator has an annular air gap disposed within a central interior space of the coil concentric with the centerline. The valve further comprises an armature that comprises an annular wall disposed in the air gap concentric with the centerline and that is displaced along the centerline as a function of magnetic flux created in the air gap by electric current in the coil to operate the valve element. The air gap is cooperatively defined by juxtaposed walls of the stator that are concentric with the centerline and spaced apart radially a distance greater than radial thickness of the annular wall of the armature, and the annular wall of the armature is disposed radially intermediate the stator walls and spaced radially from each stator wall.
Another general aspect relates to an emission control valve as just described wherein the valve forms part of an exhaust gas recirculation system of an internal combustion engine.
Still another aspect relates to an emission control comprising a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is biased closed and selectively operated to selectively restrict the passage, an electric actuator comprising a solenoid for selectively operating the valve element, and an armature that is displaced to selectively operate the valve element by magnetic force created by electric current in the solenoid, wherein the magnetic force decreases as a function of unit current in the coil over a range of initial armature displacements. A lost-motion is present in an operative coupling of the armature to the valve element to prevent the armature from operating the valve element until the armature has been displaced beyond the range of initial displacements.
Other principal aspects, features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.